Orthorhombic Polymorph of ErP5O14, Crystal Structure and Characterization

Abstract Erbium pentaphosphate crystals have been characterized and the structure of the orthorhombic polymorph (type III) determined by X‐rays. It has been found that the orthorhombic samples of ErP5O14, space group Pnma, crystallize mainly at higher temperatures and usually are much larger than monoclinic crystals, space group C2/c, obtained from lower‐temperature crystallizations. Differences in fluorescence and upconversion properties between orthorhombic and monoclinic polymorphs have been detected.